1. Technical Field of the Invention
This invention relates to engine design and conversions and in particular relates to the conversion of diesel engines to Otto cycle operation. We will describe the use of gas as a fuel, but the same concept can be used for other alternative fuels, such as alcohol, or even petrol.
2. Description of the Prior Art
For many years it was believed that diesel engines were effectively non-polluting as far as particulates, smoke and oxides of nitrogen emissions were concerned, but it has been found that as the engines become more fuel efficient they also become more polluting and this has led to concern, particularly in cities where large numbers of diesel engined vehicles operate.
In the cities, the major users of diesel fuel are buses and thus a major part of pollution by diesel exhausts is caused by buses. There are, of course, also major fleets of buses in inter city operation, and substantial numbers of diesel powered transport vehicles in operation both in cities and inter city operation and substantial numbers of diesel powered vehicles in such operation.
The situation as far as pollution is concerned can be exacerbated if the city has an inversion layer, such as is the case in Melbourne, where there can be a substantial build up of photochemical smog if there are periods of low wind, particularly periods where there are low winds with no or only a small northerly component. It is obviously not feasible, in the short to medium term, to replace existing diesel buses or even their engines to minimize the problem of pollution. Similarly, it is not feasible to replace prime movers or their engines.
The object of the present invention is to provide a means whereby diesel engines can be converted to operate on gaseous fuels without losing any degree of power or substantially increasingly operating costs of the engine.
The invention in its broadest sense comprises an internal combustion Otto cycle engine having located between the engine block and the cylinder head a spacer plate which is so formed that as the combustion charge is passed into the engine and compressed, it is caused to move in such a way that a substantial part of the charge moves over the spark plug during an ignition event.
In a preferred form of the invention, the engine is an engine originally designed to operate on a diesel cycle modified to use a gaseous fuel
The plate may be formed so that there is an extension over at least part of the inlet valve so that as the combustion charge enters the combustion chamber its direction of flow is diverted so effectively the whole of the charge is directed to the cylinder or cylinder head wall at an angle so that it spirals down the cylinder.
In a particular form of the invention where there are two inlet valves, one of the valves may be largely occluded by a member passing over the top thereof which increases the swirling of the charge.
The spark plug may preferably be located in what is the injector hole of the cylinder when the engine is being used with diesel fuel.
It is also preferred that an annular internal extension on the spacer plate and the upper end of the piston is relieved with an annular frusto-conical end which is adapted when the piston at its upper extremity of the stroke to terminate closely against the extension.
In another aspect of the invention, we provide a spacer plate to be connected between the engine block and the cylinder head of a diesel engine which spacer plate acts to reduce the compression ratio in the engine and which is internally formed so that as the charge air passes into the cylinder from the inlet valve or valves it is cause to move around the periphery of the cylinder and, because of frictional forces as well as the energy contained in the combustion charge, the whole body of gas tends to swirl.
The invention also includes a gas fuel engine having such a spacer plate between the engine block and the cylinder head.
In order that the invention may be more readily understood we shall describe with reference to the accompanying drawings, one particular embodiment of the invention.